Apparatus for measuring electric energy



July 25, 1939. D. SCIAKY 2,157,553

APPARATUS FOR MEASURING ELECTRIC ENERGY Original Filed Aug. 6, 1934 2 Shets-Sheet 2 David SCIQKS I VENT E Patented July 25, 1939 I amass I arraaa'ros ron MEASURING iimic'riuo macs I UNITED. STATES PATENT OFFICE;

David Sclaky, Paris, France Original application August 6, 1934, Serial No. 738,647. Divided and this application April 23, 1986, Serial No. 75,977. In France August 18,

I Claims. (Cl. 171-95) 4 The present invention relates to an apparatus In fact, the device according to the invention for measuring the energy developed at the weldmeasures ing point of a welding circuit for the purpose of t obtaining accurate indications as to the-energy I 5 developed at the welding point in spite of the errors introduced due to the fact that the wherein, however "does not represent the input measuring instrument cannot be connected to the potential dmerence but rather theyoltage at inaccessible points proper where the welding the points of application of electrodes to the energy is actually developed but must be connected metal sheets t0 be Welded- I w to points which are easily access1b1e It is known that, if the current which serves The present invention is a for Operating the device, iS 8.11 alternating and application, Ser. No. 738,647,1lled August 6, 1934, sinusoidal the above'mentiqned integral and issued into Patent 2,054,343. function gives It has been proposedto control, by various 5 is means, both the conditions attending electric r,

ot e1 er tion a l t zgond i ng i ig r t on of tlie xfiazl i iiig T fithf e ifd In other wordsthe angle is thus Introduced thermic or magnetic ammeters are generally used, which corresponds to the phase shifting between which measure either. the voltage and the current.

In practice it is very dimcult to connect the It, measuring coil at the electrode points, which are t; 1 inaccessible. One object ofthe present invention is to overt v come the above described difllculties. I A rurther object of the invention is to devise an or even apparatus for the measurement of the energy developed at the welding point of an electric welding circuit. I ti A still further object of the invention is to n being the time element at the beginning of the obtain in a measuring s m f h p exa welding, ts being the time eleme t at th d of indications of the real energy utilized at the the operation, 1' the intensity of the welding'curwelding p n n p t f th r s due t the rent and u the voltage at the terminals ofthe fact that the measuring instrument cannot be source of energy at any given moment. connected to the electrodes pinching the work If only Jidt or fi'dt is measured, it is admitted pieces a between which t energy f the w d 35 that the power dissipated in the welding operais developed, as these electrodes are inaccessible tion is a function of the intensity of the current bu mus h branched t accessible points spa because, inasmuch as the potential difierence o the electrodesin the feeding circuit remains constant, only the Th j s of the p i v ti ar a m- 40 resistance during the welding intervenes to modp s ed y apparatus cr e i t e f l owi ify the current intensity. specification, set forth in the appended claims In either case the measurement is not accurate, and illustratively exemplified in e pa ybecause the length and the form of the arms of 8 drawings, i which the welding tongues as well as the presence oi Fig. 1 shows diagrammatically a method of pieces of magnetic metal in the arms of the connecting a voltage coil of a wattmeter to 8.0- 5

welding machine considerably modify the power cessible P s O a Welding C H applied in the use of a given current. Fig. 2 is a tension diagram of the current Contrary to the said known procedures, the measured according to the present invention, present invention relates to an electric welding Fig. 3 is the simplified diagram of a wiring 5 device which is characterized by the fact that circuit for carrying out a measurement according the energy, which is developed during the weldto the invention,

ing operation proper,.is measured by causing the Fig. 4 is a perspective view of a wattmeter acvoltage present at the points or application of the cording to the invention connected in a diagramelectrodes to the metal sheets to be welded to matically indicated welding circuit, and take part in the measurement, Fig. 51s a simplified wiring diagram of a modified embodiment of a measuring circuit according to the invention.

As shown in Fig. 1, the voltage coil of a wattmeter G is connected'to two points C and D which are accessible and spaced from the electrodes A and B. The measured tension vi'is thus difierent from the tension 12 between the electrodes A and B. The conductor elements CA and BD introduce into the measurement errors, which are caused by the ohmic resistance and the selfinduction of said elements.

According to the present invention, the inexact tenslon 01 is corrected by subjecting it to an initial phase shifting (p0 relative to the welding current passing through the current circuit of the wattmeter. Thus, in the measurement, the

tension '0 is replaced by a tension or tapped at two easily accessible points C and D, the wattmeter being .designed not for measuring 111 cos o, but for measuring a function: v11 cos o) the angle o compensating for the error introduced by the conductors CA and DB of the machine.

Fig. 2 represents, in conformity with the usual rules of electro-technics, the principle according to which the correction of 'the inexact tension in tapped at the accessible points C and D oi the welding circuit is effected.

In the diagram of Fig. 2, I is the vector representing the intensity oi. the current at the weld- Ing point, 12 is the tension; magnitude and phase, between the electrodes A and B. This tension is to be measured, but it is inaccessible. in is the tension, magnitude and phase, at the points C and D of the feed circuit; this tension is accessible.

In passing through the work pieces to be welded, the current intensity I is subject to a variable phase shifting (p with respect to the voltage 12. The amount of this phase shifting depends upon the pressure of the electrodes and upon the magnetic (inductive) properties of the material c treated. The'variable angle o is that which must be taken into consideration'in the wattmeter.'

The tension or, which acts in the wattmeter differs from v by a quantity equal to the complex voltage drop which occurs between the accessible tapping points C, D and the. electrodes points A, B.

This tension drop is composed of an active quantity RI (R being the resistance of the two conductors sectors CA and DB) and of a reactive quantity wLXI, inadvance of with respect to the current I due to the pieces of magnetic material situated in the neighbourhood of said conductors. The resultant of these two values, proportional to the impedance of the gLr/isidered section, isrepresented by the vector The values R and Lu are known and serve todetermine the initial phase shifting (p0 to be introduced into the measurement.

The tension or utilized in the wattmeter is thus the geometricsum 'ofthe tension 12 and the addiductive tension drop in the conductors CA and BD of the machine.

The invention may be carried out by means of a device comprising a working circuit. including the welding electrodes, 9. wattmetershunted to circuit, to which is branched the primary wind-. ing I0 of a transformer I0-2 by means of variable switch If. The secondary 2 of the transformer supplies current to the welding machine controlled by a chronometric interrupter I2 driven by a synchronous motor I3. The motor I3 actuates a cam I4 for the exact regulation of the time during which the welding circuit remains closed.

The welding circuit comprises the conductors ClC, CA and DB for feeding the current to the electrodes A and B.

G denotes the assembly of electric circuits constituting the wattmeter which serves for measuring the energy developed at the welding point. The wattmeter G comprises a current coil I03 branched to the welding circuit by means of a' calibrated shunt K, a principal tension coil 61 connected to the tappingpoints C and D and a corrective tension coil 10 connected to the points C1 and Cot one 01' the feeding conductors in such a manner, that the corrective coil at any moment of the welding operation is traversed by a current in opposite direction to that which -passes through the principal tension coil 81.

Generally, the conductor 010 may have electrical characteristics different from those of the conductors CA and BD. In this case it is necessary to introduce into the circuit of the'coil I0 means for producing an initial phase shifting (p0 corresponding to that created by the inactive conductors of the machine. Any purely conven-' tional phase-shifting means may serve the purpose, as for instance, as adjustable reactance 20I and a rheostat I9.

The current coil I03 of the wattmeter excites an iron core I03, which acts upon the two parallel disposed tension coils I and 10.

The wattmeter illustrated in Fig. 4 comprises the same elements as the device G of Fig. 3, i.- e.

a a current coil I03 wound upon a magnetic core I03 shaped as a ring interrupted by a gap 65. The slotted portion 01' the core I03 projects through a window provided in the insulating plate 66. The current coil I03 is connected to the working circuit by means of a calibrated shunt K.

The principal tension coil of the wattmeter is constituted by a metallic band 61 arranged edgewise in the air gap of the core I03 and forming a halt-turn. The ends of said band are twisted .to lie flat in front of the-small plates 60, 60' and I50 which are mounted on the insulating plate and to which said band ends are secured by means of spring blades 00, 0|, 02. The electrical connection is insured by means of small'plaited cables 69. The corrective tension coil 10 of the moving coil unit is formed in the same manner as the principal voltage coil 61. The corrective coil 10 is connected at one end to the terminal or plate 68. connected in turn to the tapping point C, and at its other end to the point C1 disposed at a point spaced from C by means'of the plate 682 and the devices 10-20l regulating the 1 common plate 68' being secured solidly together,

as these ends are mounted on the same spring blade 80. The fact that the other ends of the two bands are separate and connected to difierentplates 68 and 682 does'not prevent the metallic bands 61-10 from being deflected under the influence of the magnetic field produced in the gap 65 simultaneously'and as a unit.

The axis about which the moving coil unit 61-10 oscillates is defined by the front edges of the plates 68', 68 and 66: in contact with the spring blades 80, BI, 02.

The winding of the current coil l3 and the connections of'the bands 61, 10 to the working circuit are arranged in such' a manner that the resulting deflecting force exerted by the magnetic field of the core I03 on the movable coil unit has the direction of the dot and dash arrow f in Figure 4.

The wattmeter of Fig. 4, which is of the elec-,

trodynamic type, operates'as follows: The direction of the current I traversing the current coil is chosen in such a manner that the constant magnetic field set up in the gap 65 is represented by the dot and dash vector H.

The current traversing the metallic band 61 (main voltage circuit) is represented by the dot and dash vector 11. Then, according to Amperes law, the force exerted by themagnetic field H on the band 61 traversed by the current I1 can be represented by the vertically downward directed dot and dash vector F1.

The current I2 traverses the band 10 in a direction opposite to that of 11, and the band 10 is thus subjected, on account of the field H, to an upwardly directed force F: having an absolute valuegreatly inferior to that of F1. The resultant mechanical action F is in each case equal to the arithmetic difference Fl--F2 (algebraic sum).

However, as 11 and I2 are two sinusoidal values, having their relative phases shifted an angle 'y 90 and close to 180, which angle is in fact 'y= f++complementary angle of 1p" (see diagram of Fig. 2), the forces F1 and F2 vary in an opposite sense during the passageof the welding current.

The numerical value of the resultant force F which acts on the movable coil unit 61-10 is approximately equal to can be used, in which H is assumed as being uniform.

The above described moving coil unit engages,

in rest position, two symmetrically located screws 1| (only one of which is shown) each of which extends through a bracket fixed to the insulating plate 66. The movable coil unit is provided on either side with an arm 13 adapted to act through an insulating finger 14 to close a pair of contacts 15. The contacts 15 are arranged in such a manner that either one pair of them or both pairs are closed depending upon the amplitude of displacement of the moving coil unit.

It is advantageous to choose the mechanical characteristics of the spring blades 80, -ill, 82

supporting the conductive bands 61 and 10 and the inertia of said bands relative to the axis of displacement in such a manner, that the movable coil unit of the wattmeter has a ballistic nature, i. e., has an oscillation period which is very great relative to the length of the time during which the displacing force is applied, 1. e. relative to the duration of passage of the welding current, which latter is a small fraction of a second.

It is known, that in ballistic wattmeters, the

inertia of the movable coil unit fsuiiices to en-' large the kinetic energy mv. 2) developed during the extremely short time'of the welding operation and to eifectively start its deflection when the welding itself has already been completed.

Instrumentsof this type measure exactly the electric energy expended, i. e., the product of power and duration of application 1 The arrangement of a ballistic wattmeter provides for exact measurement of the energy even if the time of the welding operations is extremely short, as for instance one twenty-fifth of a second.

The welding machine, the wiring diagram of which is illustrated in Fig. 5, has the advantage to automatically compensate the error due to the position of the tapping points C, D, spaced from the electrode points A, B.

In this arrangement, the arms CA and DB have the same total length as the circuit section DDi of the conductor, to the extremities of which section the corrective coil 10 of the wattmeter G is connected. As the cross-section of the conductors is constant, the sectors CA-i-DB and DD]. have the same ohmic resistance. Moreover, these conductor sectors are disposed, in the assembly of the welding machine, in such a manner that they are subject to equal self-induction owing to the pieces of magnetic material disposed in the neighbourhood of the sectors. In this arrangement, there will be phase shiftings of equal value between the tappingpoints CD and the electrodes on the one hand and. between the tapping points D and D1 on the other hand. Consequently, whatever the value of the welding current will be, the corrective tension acting in the coil 10 will be automatically determined by the voltage drop between D1 and D equal to RI in the arms CA, DB, and by a phase difference relative to the current I according to the formula B. being the ohmic resistance in the conductors CA and DB, L being their self-induction and 0111 being their reactance.

I claim:

1. In an electric welding device a working circuit comprising welding electrodes, a wattmeter,

having a current coil in shunt with said working circuit and two voltage coils, one of said volt- I age coils being branched to said working circuit at two accessible tapping points on opposite sides of and spaced from the electrode points and a corrective voltage circuit including the second voltage coil and a phase shifting means and being connected to two accessible points of the working circuit at one and the same side of the electrodes, said corrective circuit being arranged and adapted to transmit to said second voltage coil a tension equal and opposed to the complex ohmicand inductive voltage drop occurring between said tapping points and said electrode points.

2. A device, as claimed in claim 1, in which the part oi the working circuit between said tapping points for the first voltage coil and the part oi the working circuit between the points, to which said corrective circuit is connected, have equal ohmic resistances and are disposed in the device to be'subject to equal magnetic inductances due to the presence ofmagnetie masses in the neighbourhood of the working circuit.

3. A device, as claimed in claim 1, in which said wattmeter is formed as a ballistic wattmeter. 4. A device, as claimed in claim 1, in which said wattmeter comprises a magnetic core upon rier for said two voltage coils, said common carrier being movable with respect to said current DAVID SCIAKY. 

